Tension control apparatus for flexible support strands of an extensible conveyor



c. T. OGDEN 2,858,936 TENSION CONTROL APPARATUS FOR FLEXIBLE SUPPORTNov. 4, 1958 STRANDS OF AN EXTENSIBLE CONVEYOR 2 Sheets-Sheet 1 FiledJan. 15, 1958 mmvmze Charles T Ogden ATTORNEY 5 .Eofiaw 20 2065; @v

NOV. 4, 1958 Q 1-, OGDEN 2,858,936

' TENSION CONTROL APPARATUS FOR FLEXIBLE SUPPORT STRANDS OF ANEXTENSIBLE CONVEYOR Filed Jan. 15, 1958 2 Sheets-Sheet 2 14a 75/ I521I36 m 26 64 I I26 12 w 52 i 3/ 124 a0 68 J F F 128 I Fig 6 67 ,6? 78 77/09 1/3 I06 72 9/ 99 1/7 1/3 as 57 I04 1/8 107 55 I! a 1 84 I" m 49 J 699 89 56 4 6 92 I08 --INVENTOR.

8573 7987 8/ 82 //4 I T O I. 9 ar es g en Fig. '4, Q0 28 5 V ATTOR/VEVTENSION CONTROL APPARATUS FOR FLEXIBLE gligflagzRT STRANDS OF ANEXTENSIBLE CON- Charies T. Ogden, Chicago, 'Ill., assignor to GoodmanManufacturing Company, Chicago, Ill., a corporation of IllinoisContinuation of abandoned application Serial No. 581,195, April 27,1956. This application January 15, 1958, Serial No. 709,436

14 Claims. (Cl. 198-208) This invention relates generally to conveyors,and particularly to an improved extensible conveyor which can beextended and retracted even during the conveying operation. This is acontinuation of Charles T. Ogden application Serial No. 581,195, filedApril 27, 1956, now abandoned.

The invention relates to a flexible strand sideframe conveyor which hasstrand means, such as a pair of wire ropes or equivalent strands,trained along a course and on which are supported rollers for anorbitally movable conveyor belt. In the case of an extensible conveyorsuch as the present one, the inbye ends of the wire ropes are wound on aconveyor tail section which is provided with means for tramming ittoward a mine face to follow a mining operation. The ends of the ropesremote from the tail section are fixed in some suitable way. The tailsection has strand tensioning means which maintains" the tension in thewire ropes at a preselected value to support the rollers, the belting,and the load thereon. The strand tensioning means pays out the ropes asthe tail section is advanced inbye and winds in the ropes as the tailsection is moved outbye. The belt itself is normally provided with anexpandable and contractible loopwhich varies to accommodate the lengthrequirements ofthe conveyor. a

In the past, strand tensioning means has been provided which operatesautomatically between upper and lower tension limits. to extend theconveyor, it first increases the tension to its upper limit, at whichthe automatic tensioning means comes into operation and pays off thestrands at such upper tension limits. And, when the tail is reversed, toshorten the conveyor, it decreases the tension to its lower limit atwhich the tensioning means winds in the strands. Normally when the tailis stationary the strand means will be tensioned somewhere between theselimits, the tension varying up and down in accordance with the load onthe belt. The upper and lower tension limits will be preselected toaccommodate maximum and minimum belt loading.

The tension in the strands works against the tramming mechanism when thetail is moved in a forward direction,

namely the direction to lengthen the conveyor. That is,

the strands hold back while the tramming means is attempting to move thetail forward.

When the tail is trammed forward, the strand tension required to supportthe load during the tramming operation is usually no more than thetension existing at the beginning of trammingv actuation. To let thetension go any higher merely adds to the work that the trammingmechanism must do and often causes the tram wheels or crawlers to spinif the ground is slippery.

Accordingly, it is a primary object of the present invention to providecontrol means for the strand tensioning means which is effective, duringtramming, to maintain in the strands whatever tension was inthe strandsat the beginning of the tramming operation.

Another object is the provision of strand tensioning Thus when the tailis trammed forward 2 control means including sensingme'ans for sensingthe initial value of tension in the strands at the beginning ofactuation of the tramming means and control means for the strandtensioning means operable in response to the sensing means to maintainthe tension at such initial value during actuation of the trammingmeans.

Another objectis-the provision of improved strand tensioning'controlmeans including means for sensing the. initial strand tension at thebeginning of actuation of the.

tramming means, memory means effective to storeinformation as to thevalue of such initial tension, and means controlled by such memory meansfor maintainingjt he, strands at such initial tension during thetramming actu ation.

The invention is particularly directed to apparatus-for controllingwithin desired limits the tension in the sup-. port strands of anextensible strand sideframe conveyor,

it being understood that the term ,extensible includes.

conveyors that are contractible.-, Since-the loading of the conveyingreach of such conveyor varies within wide limits, the tension in thesupport strands will vary in accordance with the load. In oneapplication of such conveyors, the support strands may be mounted atinter: vals of about ten feet upon standards, and troughing rollerassemblies may be mounted at about five foot tervals intermediate thesupport standards. The extensible conveyor may be of the type where atleast one of the end sections, preferably the tail or inbye section, isarranged to move upon endless crawler treads. The two support strandsmay be wound ,upon storage reels mounted on such end section and drivenby hydraulic motors.

One of the problems attendant upon tramming such end section inaccordance with the increase 'in length of in the cables just prior tothe tramming operation. suchchanges in tension imposes dilferent loadson the support: strands, and the change in deformation throughout thelength of the strands may be such as to cause tipping of the standards.By way of example, the change in deformation in a ten foot length ofstrand upon a change in tension of from 1200 pounds to 2400 pounds maybe as much as 0.4", and in a conveyor 1000 long the total deformationmay amount to 40".

If the support strands are anchored atop the support standards, some ofthe standards, particularly at the end of the conveyor line, must berequiredto move through the 40" distance. In View of the fact that themine floor is irregular, the standards do not slide upon the floorfreely but may instead be caused to tip, eventually to fall, if notwatched closely. y

With the foregoing considerationsjin mind it is an important object ofthis invention to provide apparatus for paying out and reeling in theflexible strands, such paying out and reeling in being within desiredlimits of tension at all times.

Another object is to provide automatic control appa ratus which willinsure that the tension obtainingfin thestrands at the start of atramming operation will be maintained all during such trammingoperation.

It is a further object to measure the tension in the support strands,and to apply such measured value to a' control circuit which will reelin or pay out only at the predetermined measured value.

Other object and important features. of the invention will be apparentfrom a study of the specification following taken with the drawingswhich together show a preferred embodiment of the invention, and what isnow considered to be the best mode of. practicing the principlesthereof; Other embodimentsmay be suggested to those having the benefitof the teachings herein, and such other embodiments are intended to bereserved especially as they fall within the purview and spirit of thesubjoined claims.

In the drawings:

Fig. l is a side elevational view of the tail section of an extensibleand retractible conveyor having the improvernents accordingto thepresent invention embodied therein; 1

Fig. 1a isa side elevational view of a complete extensible conveyor,having a tail as seen in Fig. l, and having the improvements accordingto the present invention embodied therein;

Fig. 2 is an enlarged fragmentary view of- Fig. 1 showing apparatusforcontrolling'the paying out of support strand for. the conveyor seenin Fig. 1 when the tension reaches. an upper limit;

Fig. 3 is a view similar to Fig. 2, but showing how the mechanism ofFig. 2 operates to wind in the support strand when the tension thereinreaches a lower limit;

Fig. 4 is a longitudinal sectional view taken through a control valveemployed with the apparatus of Figs. 2 and3', said control valve beingoperable to control the windingin and paying out of support strands;

Fig. 5' is a plan view of an alternate form of apparatus forcontrolling'the tension in the support strands; and

Fig. 6 is a-schematic diagram of a hydraulic control circuit for thetramming motor of the tail section seen in Fig. 1, and showing aconnection from such circuit to the apparatus of Figs. 2 and 3 tomaintain the tension in the supportstrands at the value obtaining at thestart of the tramming operation.

Referring now to Figs. 1 and la of'the drawings, the present inventionis embodied in anextensible conveyor indicated generally by thereference numeral 10.- The conveyor includes atail section- 11 and ahead .section 11a mounted for movement respectively uponcrawler treads12 and 12a. The tail section 11. forms a means for reversingan-orbitally movable conveyor belt having a conveying reach 13- and areturn reach 14.

The conveying reach 13. is supported upon spaced flexible strands16, andthese strands are spanned; by idler roller assemblies indicatedgenerally by the reference numeral 17, the idler roller assemblies 17being spaced throughout the length of the conveyor reach 13 for supportthereof. Support-standards 15 are disposed at intervals throughout thelength of the support strands 16 for support thereof. A belt storageloop 20, disposed in the return reach 14 adjacent the head section 11a,is arranged to be lengthened or shortened according to the requiredlength of the conveyor 10. Details of construction of such a conveyorand the strand supporting arrangement are shown in more detail in Craggset a1. U. S. Patent No. 2,773,257.

As seen in Fig. 1a, the support strands 16 are fixed at a locationremote from the tail section, in this case by mounting them on the headsection 11a. As seen in Fig. 1, the support strands 16 are reeved'around a pair of snubbing sheaves 18 and 19. Thesnubbing sheaves 18 and19 turn upon stub shafts 21 and 22 respectively whichextend from asupport plate 23 pivoting about a center corresponding to the stub shaft22 and supported thereon. Shaft 22 extends from a side frame of the tailsection 11.

Each support strand 16 is stored upon a storage reel 26 mounted uponashaft 27 extending from side frame As seen in Fig. 1, the control of thetramming ofthe tail section 11 is by a pair of forward and reversetramming valves 31 (see also Fig. 6) which control the direction ofoperation of a crawler tread drive motor 30.

The tension in the support strands 16 varies in accordance with the loadon the conveying reach. While the tension is kept within desired limitsthe variation in tension is not critical excepting for times when thetail section 11 is trammed in one direction or another. It is importantat such times to maintain the tension in the strands 16 at the valuethen obtaining at the start of the tramming operation. Failure tomaintain the tension in the strands results in shifting of the strandsupports 15.

Means are accordingly provided to maintain the tension of the supportstrands within desired limits, but more important, to maintain thetension at the value then obtaining at the start of the trammingoperation for the reasons above.

Structure functioning for both of said purposes will now be described.

The support 23 for the snubbing sheaves 18 and 19 is limited in itsmovement by means of a spring 35 having one end abutting a stop 32 whichcan be held in an adjusted position by means of adjusting screws 33. Theother end of the spring 35 abuts an extension34 of the support 23, andit will be seen that the spring 35 restrains the free movement of thesupport 23 in a counterclockwise direction by bucking the tension instrand 16. Thus, it will be seen that the spring-biased support 23comprises a strand tension responsive member which is movable inaccordance with the tension in the strand.

Increase in tension upon a strand 16 in excess of a predetermined amountcauses the corresponding support 23 to rock in a counterclockwisedirection, thereby actuating the valve 29to control the direction ofoperation of motor 28, as will now be described.

Control'of the valve 29 is had by an actuating rod 36 which isresiliently connected to the support,23 through a spring 37 bottomed atan end 38 of a cylindrical spring housing 39. The other end of thespring 37 is provided with a-washer 41, the end of the rod' 36 beingthreaded to receive a nut 42 hearing against washer 41,which normally isin abutting relationship with a stop flange 43 within the cylindricalhousing 39- The other end portion 44 of the cylindrical housing 39 ispivotally connected at 46 to-the support 23. The load in the spring 37fthus enables the support 23 to movev the actuating rod 36, at the sametime being available to absorb impact and protect the control mechanismfrom destructive shocks, for instance in case, of sudden breakage of thestrand 16 or overloading beyond a predetermined maximum limit.

The actuating rod 36 has a clevis 47 which is pivotally connected at 48to an intermediate portion of an operating lever 49. One end of themovable operating or control lever 49'is pivotally connected at 51 to alongitudinally shiftable abutment rod 52, the rod 52 passing throughguides 53 and 54 which are mounted on the tail side plate 24-. As willbe seen, the rod 52 comprises part of a memory system for storinginformation relating to the strand tension.

When the tail section 11 is stationary, the tension in the strand 16 mayvary within limits as determined by the loading on the conveying reach13. Increase in strand tension causes the tension responsive support 23to rock in -acounterclockwise direction against the compression in thespring 35. Such movement of the support 23 will cause the lever 49 torock about one or the other of pivots 51 and 56 depending on theirrespective resistances to movement as will be hereinafter explained. Thepivot pin at 56 is attached to a clevis 57 extending from a spool valvemember 58 of the control valve 29. As will be seen, the valve spool 58is urged to a centered position by centering spring means which,afr'ords more resistance to movement of pivot 56 than is afforded thepivot 51 when the rod'52.is free to slide. This occurs when the tail isstationary so that movement of the tension responsive member 23 istransmitted through the actuating rod 36 into pivoting of the controllever 49 about pin 56 while freely sliding the memory rod 52 within itsguides 53, 54.

The movable memory abutment rod 52 carries a pair of adjustable stops 59and 61 threaded thereon. The abutment rod 52 under the conditionsdescribed is thus free to shift to a high limit position, with theadjustable stop 59 against the fixed guide 53 as shown in Fig. 2 to marka high limit of tension in the support strand 16; or to a low limitposition with the adjustable stop 61 engaging the guide 53 to mark a lowlimit as shown in Fig. 3.

Shifting of the support 23 in a counterclockwise direction after thehigh limit stop 59 engages the guide 53 causes the lever 49 to rockabout the pivot point 51 and to move the valve spool 58 to the left tocontrol the flow of fluid to the motor 28 and cause the storage reel 26to pay cable therefrom.

Conversely, see Fig. 3, movement of the support 23 in a clockwisedirection first causes the low limit stop 61 to engage the fixed guide53, the lever 49 thereafter rocking about the pivot point 51 and causingmovement of the valve spool 58 to the right, to direct fluid to themotor 28 in an opposite direction to cause the storage reel 26 to Windcable thereon until the tension is restored to a value within thedesired range predetermined between the stops 59 and 61.

Referring now to Fig. 4 of the drawings, the control valve 29 isconnected in a circuit which includes a pump 62 which receives fluidfrom a tank 63 by means of a line 64. The output from the pump 62 isconnected in a pressure line 66 having a pressure relief valve 67therein, excess of pressure being relieved by a line 68 to the tank 63.

The control valve 29 includes a cylindrical bore 71 therein. The valvespool 58 is slidable within the bore 71,.and has an end land 72,intermediate lands 73, 74 and 76, the land 76 being flanked by anopposite end land 77. Lands 72 and 73 are spaced by a portion 78 ofreduced diameter. Lands 73 and 74 are spaced by a portion 79 of reduceddiameter. Lands 74 and 76 are likewise spaced by a portion 81 of reduceddiameter, and lands 76 and 77 are spaced by a portion 82 of reduceddiameter.

The valve body 69 has a pressure port 83 which is nora valve body 69having mally lapped by the land 74. Lands 84,. 85, 86 and 87 define atank port 88, a working port 89 and a port 91 to one side of thepressure port 83. Lands 92, 93, 94 and 96 define a tank port 97, aworking port 98 and a port 99 to the other side of the pressure port 83.

A cylindrical bore 101 within the spool 58 is intersected by cross bores102 and 103 to cause communication between the tank port 97 and tankport 88. r

The left end of valve spool 58 is encircled by a spring 104 bearingagainst a shoulder 106 on the valve spool 58 and having its other endbearing against an end cap 107 fastened as by cap screws 69, the end cap107 enclosing one end of the valve spool 58. I

The opposite end of the valve spool 58 passes through .an end cap 108held tothe body 69 by cap screws 109. The valve spool 58 is maintainedin the centered position shown in Fig. 4 by means of a washer 111normally bearing against a shoulder 112 in the end cap' 108, the washerat times bearing against a C-ring 113 on the spool 58. Movement of thevalve plunger 58 to the left is opposed by a spring 114 guided upon asleeve 116 and abutting a washer 117 bearing against the right end ofthe valve body 69. The washer 117, during the movement of the valvespool 58 to the right, engages a shoulder 118 on the valve spool 58, andduring movement of the valve spool 58 to the left the washer 111-isengaged by the C-ring 113. Movement in either direc tion is opposed bythe centering spring 114. Thus it (not shown) to the valve bodyv will beseen that the spool member 58 comprises a por tion of the tensioncontrol means which is movable for selectively increasing and decreasingthe tension in the corresponding strand.

Consider now the condition of Fig. 3, when the low limit stop 61 is inengagement with the guide 53, and the lever 49 is being rocked in aclockwise direction about pivot 51 to move the spool 58 to the light.This occurs when the tension in strand '16 is below a valuepredetermined by the setting of stop 61. Under such condition the lands74 and 73 on the valve spool 58 will unlap their respective lands 86 and87 in the valve body 69, to cause pressure fluid to flow from thepressure port 83 to the working' port 89,'working port 89 beingconnected by a Working line 90 to the fluid motor 28. During suchmovement land 93 will be unlapped and the exhaust side of the motor 28will have its line 95 connected to the tank port 97, the spent fluidpassing by way of the bore 101 through the spool 58 to be exhausted' atthe tank port 88 which is connected by a line 100 to the tank 63.

. The motor 28will accordingly be driven in a direction to wind thestrand 16 onto the reel 26, and restore the tension, while rocking thesupport 23 in a clockwise direction until the spool 58 returns to itscentered (Fig. 4) position. j j I Conversely, when the high limit stop59 engages the guide 53 and the support is continuing itscounterclockwise movement by reason of tension in the strand 16 risingabove the setting of the stop 59, the spool 58 will be shiftedto theleft. This will cause lands 74 and 76 on the valve spool 58 to unlap therespective lands 96 and 94 in the valve body 69 supplying pressure fluidfrom the pump 62 to the working port 98 and thence to the line 95 todrive the motor 28 in the opposite direction and pay strand from thereel26.

Under such condition line 90 becomes the exhaust line from the .motor28, and land 72 on the valve spool 58 unlaps the land 85 in the valvebody 69, the spent fluid returning to: the tank 63 by way of the tankport 88 andthe return line 100.

When the tension in strand 16 is thus reduced to a desired value thevalve 29 will return to the centered position seen in Fig. 4.

If the tension rise is slow enough, the same correction may be made bysimply shifting the spool 58 back to its centered (Fig. 4) position,normal leakage through the valve providing the strand payoff necessaryto restore normal tension.

The conditions described for the shifting of the support 23 and theoperation of the valve 29 are normal when the tail section 11 is.in a.stationary position. When the tail section is moved, it is important tomaintain the same tension in the strand means 16, so as to preventdisplacement, tipping, :or walking of the strand support standards 15.To this end, there is provided means for freezing or locking the memoryabutment rod 52 in place at the beginning of tramming actuation. Thisserves to store information as to the initial value of the tension atthe beginning of the tramming operation and provides a reference againstwhich the tension may be automatically maintained at such initial valuewhile tramming.

Referring now to Fig. 6 of the drawings, the control valve 31 controlstramming movement of the tail section by controlling operation of thecrawler tread 12. A second valve 31 '(Fig. 1) may be used to controltramming of a crawler system on the other side of the tail section. Thecontrol valve is connected by a pressure line 121 to the output from thepump 62 which may be the same as that shown in Fig. 4. The valve 31 hasa working line 122 connected to the crawler tread drive motor 30 fordriving the crawler tread 12. The spent fluid from motor 30 returns tothe valve 31 by means of a line124, and to the tank 63 by a tank returnline 126."

A shuttle valve 127 is connected across the lines 122 and124', andis'provided with shuttle ball 128 therein which-shifts to one position ortheother depending upon the direction of operationcalledfor inthe-crawler tread drive motor 30. It will be understood that the valve31 is of the reversible type, to cause the working lines 1 22- and 124'to alternate as exhaust lines from the motor 36 depending-upon itsdirection of operation.

In either direction of operation, the shuttle valve 127 operates tocause fluid to be delivered to a line- 129 to movea-piston 131*within abrakecylinder 132 mounted on the side plate 24; A pair of guides 133 isprovided onthe end ofthe cylinder 132 through which the abutment rod 52extends.- The piston'131, movable within the cylinder 132, has anextension 134 thereon which moves against the abutment rod 52' tocauseit to be clamped tightly in theguides 133. Thus the rod 52 functions asa memory element capable of storing intelligence as to strand tensionwhen therod is fixed in place by the locking means 131-132 in responseto actuation of the tramming tread-means 12.

When the brake 132- is not actuated, the memory abutment rod 52 slidesfreely. Movement of the valve spool 58 is relatively less easy due toits centering; spring 114. Under such condition, shifting of the tensionresponsive support 23 pivots lever 49 about the pin 56.

Consider now the condition-of the support 23 as the tail section 11advances to the right as seen in Fig. 1. Such tramming operation wouldtend to impose a greater amount of tension in the strand 16 causing thesupport 23 to shift in a counterclockwise direction as seen in Fig. 2,and cause the valve spool 58 to be rocked to the left, while rockinglever 49 to.the left about pivot 51, thereby causing the valve 29 tooperate the motor 28 in a direction to drive the storage reel 26 in adirection to pay the strand 16 therefrom. It is believed evident thatsuch paying out of the strand 16 from the drum 26 would cause thetension to be relieved, and the support 23 to rock in a clockwisedirection to adopt a position corresponding to the tension thenobtaining at the start of the tramming operation. It should be notedthat the brake cylinder 132'is in the locked position as long as thetramming operation continues.

Conversely, when the trammingoperation is to the left, that is,retracting, thetension on the strand 16 will be relieved, causing thesupport 23 to rock in a clockwise direction. Under such condition thelever 49 will be rocked to the, right, about pivot 51, as seen in Fig.3, and the valve spool 58 also shifted to the right to supply fluid tothe motor 28 to drive it in a direction so as to causethe strand 16 tobe wound upon the storage reel 26. Undersuch condition, the tension inthe strand 16 will be'increased, and the support 23 will rock in acounterclockwise: direction untilj the control valve 29 isreturnedto-its centered position seen in Fig. 4.

It is believed evidentthat the-strand in either case will be maintainedat the tension then obtaining at the start of the tramming operation, beit ineither direction.

Referring now to Fig. of the drawings, there is shownanother embodimentof the-invention where the strand 16 has a greater amount of wrap aboutthe snubbing sheaves 19 and 18. Here, the support 23 rocks in ahorizontalplane about a shaft 136 mounted on'an extension 137 from theside frame 24' of the tail section 11. The rocking of the support 23 bytension in the strand is bucked by a spring 138 encircling a' rod 139pivotally connected to the support 23 by pivot pin 141. One end of thespring bears against a washer 142 held onto the rod by a nut and theother end of the spring bears against the end of an abutment cup 143carried by the side frame 24. It will beseenthat the spring 138 imposesrestraint against movement of the support 23 in a'counterclockwisedirection. 2

The support 23 in Fig. 5 has acam surface 144,.and a roller type camfollower 146 is urged by a spring 147 against the cam surface 144, thespring 147 being held betweena flange 148 on the follower 146 and afixed abutment 149 extending'from the side frame 24; The cam follower146 is cylindrical in form and'encloses the movable actuating rod 36,there being a washer 151- on the actuating rod 36 in engagement with ashoulder 153 on the cam follower'146, there also being a washer 154 onthe actuating rod 36 hearing against the end of the follower 146 remotefrom the cam surface 144. A spring 156 is compressed betweenthe twowashers 151 and 154.

it is believed apparent that the movement of the actuating rod 36 is hadthrough the spring 156 which acts as an elastic compression member.Spring 156 dampens minute movements of the actuating rod'36, so as toprevent minor movements of the valve spool 58 and consequent huntingoperation of the fluid motor 28. It also protects the control mechanismagainst suddenly applied loads as does the spring 37 in the previouslydescribed embodiment.

While the invention has been described in terms of a number ofembodiments thereof, its scope is intendedto be limited only by theclaims here appended. It will be understood that the present inventionis applicable to controlling tension in strand means whether single orplural strands are employed. In the embodiment illustrated, two strands16 are employed and the tension control means may be duplicated for bothof them where desired.

I claim as my invention:

1. In an extensible strand sideframe conveyor, a tail' section,belt-supporting strand means carried by and extending from said tailsection and being fixed at a location remote from said tail section,tramming means for moving said tail section to vary the effective lengthof said conveyor, and strand tensioning means effective to apply atension in said strand means, the improvement comprising: means foractuating said tramming means to move said tail section; sensing meansfor sensing the initial value of tension in said strand means at thebeginning of actuation of said tramming means; and control means forsaid strand tensioning means operable in response to said sensing meansto maintain the tension at said initial value during actuation of saidtramming means.

2. In an extensible strand sideframe conveyor, a tail section,belt-supporting strand means carried by and extendingfrom said tailsection and being fixed at a location remote from said tail section,tramming means for moving said tail section to vary the effective lengthof said conveyor, and strand tensioning means effective to apply atension in said strand means, the improvement comprising: means foractuating said tramming means to move said tail section; means includinga memory device operable responsive to actuation of said tramming meansto sense the initial value of strand tension at the beginning. of thetramming actuation and effective to maintain the strand tension at saidinitial value during said tramming actuation.

3. In an extensible strand sideframe conveyor, a tail section,belt-supporting strand means carried by and extending from said tailsection and being fixed at a location remote from said tail section,tramming means for moving said tail section to vary the effective lengthof saidconveyor, and strand tensioning means effective to apply atension in said strand means, the improvement comprising: means foractuating said tramming means to move said tail section; means forsensing the initial strand means tension at the beginning. of actuationof said tramming means; memory means effective to store information asto the value of said initial tension; and means controlled by saidmemory means for maintaining the strand means at said initial tensionduring the actuation of said tramming means.

4. In an extensible strand sideframe conveyor, a. tail section,belt-supportingstrand means carriedby and extendingfr'om said-tailsection and being fixedata locae tion, remote'from said tail section,tramming means for moving said tail section to vary the efiective lengthof said conveyor, and strand tensioning means effective to apply atension in said strand means, the improvement comprising: means foractuating said tramming means to move said tail section; said strandtensioning means effective to maintain the tension in said strand meansin a range between predetermined high and low limits; means operableresponsive to actuation of said tramming means to sense an intermediatevalue of strand tension which is intermediate said high and low limits;and means, including apparatus for storing information as to strandtension, elfective to rnaintainthe strand tension at said intermediatevalue during said tramming actuation.

5. In an extensible strand sideframe conveyor, a tail section,belt-supportingstrand means carried by and extending from said tailsection and being fixed at a location remote from said tail section,tramming means for moving said tail section to vary the eifective lengthof said conveyor, and strand tensioning means effective to apply atension in said strand means, the improvement comprising: means foractuating said tramming means to move said tail section; means forsensing the tension in the strand means including a sensing elementmovable over a range corresponding to a range of tensions; meansoperable responsive to actuation of said tramming means to hold saidsensing element in a fixed position corresponding to the initial valueof the tension in the strand means at the beginning of said trammingactuation; and control means for controlling the strand tensioning meansat a tension corresponding to said fixed position of the sensingelement, and control means being effective to maintain the strand meanstensioned at said initial value during said tramming actuation.

6. In a flexible strand sideframe conveyor; a movable end section havingextending therefrom a flexible strand adapted to support a conveyorbelt; tramming means actuatable for moving said end section; strandtensioning means efiFective to apply a tension in said strand means; astrand tension responsive member movably mounted on said end section;tension control means including a member movable between positions forselectively increasing and decreasing the tension in said strand, meansurging said tension control member to a neutral position; a movablememory element; said tension control member and memory element beinginterconnected by a lever; said tension responsive member beingconnected to said lever and effective to move said lever to move eitherthe tension control member or memory element,

whichever affords the least resistance; and locking means operable tofix the position of said memory element responsive to actuation of saidtramming means; whereby, during movement of said end section, strandtension is maintained at its value at the beginning of such movement.

7. In a flexible strand sideframe conveyor, the combination of claim 6'including means for limiting the movement of said memory elementcorresponding to preselected upper and lower limits of strand tension.

8. In a flexible strand sideframe conveyor, the combination of claim 6in which said tension control member is connected to said lever by anelastic shock-absorbing link.

9. In a flexible strand sideframe conveyor, the combination of claim 6'in which end portions of said lever are pivotally connected respectivelyto said tension control member and memory element and an intermediateportion of said lever is connected to said tension responsive member.

10. In an extensible strand sideframe conveyor, a tail section,belt-supporting strand means carried by and extending from said tailsection and being fixed at a location remote from said tail section,tramming means actuatable for moving said tail section to vary theeffective length .pf said conveyor, and strand tensioning meanselfective iii to apply atension in said strand means, the improvementcomprising: a movable tension sensing element; stop means for stoppingmovement of said sensing element at the ends of a range defined byselected high and low tension limits; auxiliary stop means operable tostop said sensing element within said range; control means for saidstrand tensioning means eflective in response to the stopping of saidsensing element to maintain tension in said strand means at a valuecorresponding to its stopped position; and means operable responsive toactuation of said tramming means to operate saidauxiliary stop means tostop said sensing element in position corresponding to the initialtension in said strand means at the beginning of tramming actuation;whereby said initial tension is maintained in said strand means duringsaid n-ammng actuation. t

11. In an extensible strand sideframe conveyor, a tail section,belt-supporting strand means carried by and ex opposite direction tobuck the tension in the strand means;

stop means for stopping movement of said sensing element at the ends ofa range defined by selected high and low tension limits; auxiliary stopmeans operable to stop said sensing element within said range; controlmeans for said strand tensioning means effective in response to thestopping of said sensing element to maintain tension in said strandmeans at a value corresponding to its stopped position; and meansoperable responsive to actuation of said tramming means to operate saidauxiliary stop means to stop said sensing element in positioncorresponding to the initial tension in said strand means at thebeginning of tramming actuation; whereby said initial tension ismaintained in said strand means during said tramming actuation.

12. In an extensible strand sideframe conveyor, a tail section,belt-supporting strand means carried by and extending from said tailsection and being fixed at a location remote from said tail ,section,tramming means actuatable for moving said tail section to vary theeifective length of said conveyor and strand tensioning means effectiveto apply a tension in said strand means, the improvement comprising: amovable tension sensing element; said sensing element being movable overa range corresponding to a range of tension in said strand means; stopmeans operable to stop said sensing element against movement within itssaid range; control means for said strand tensioning means eifective inresponse to the stopping of said sensing element to maintain tension insaid strand means at a value corresponding to its stopped position; andmeans, operable responsive to actuation of said tramming means, tooperate said stop means to stop said sensing element in positioncorresponding to the initial tension in said strand means at thebeginning of tramming actuation; whereby said initial tension ismaintained in said strand means during said tramming actuation.

13. In an extensible strand sideframe conveyor, a tail section,belt-supporting strand means carried by and extending from said tailsection and being fixed at a location remote from said tail section,tramming means actuatable for moving said tail section to vary theeifective length of said conveyor and strand tensioning means effectiveto apply a tension in said strand means, the improvement comprising: amovable member connected to said strand means for movement responsive tochange in tension in said strand means; said member having oppositelydisposed tension sensing and tension control portions, either portionbeing movable about the other portion, responsive to change in tensionin said strand means,

1 1 depending on whichever afiords the least resistance; means normallyenabling the tension sensing portion to move about the tension controlportion; meanjsiop'erable responsive to actuation of said tramming'meansfor looking said tension sensing portion in position at the,start' ofthe tramming actuation enabling the tensioncont'rol portion to moveabout said sensing portion; said tension control portion being movable,While the sensing portion is locked, between positions for selectivelyincreasing and decreasing the tension in the strand; whereby, duringtramming actuation, the tension in the strand means is automaticallymaintained at its value at the beginning of said tramming actuation.

14. In an extensible strand sideframe conveyor, a tail section;belt-supporting strand means carried by and extending from said tailsection and being fixed ata location remote from said tail section,tramming means actuatable for moving said tail section to vary theeffective length of said conveyor and strandtensioning means effectiveto apply a tension in said strand means, the improvement comprising: atension responsive member movable in accordance with the tension in saidstrand means; a control lever having a portion intermediate the endsconnected to said tension responsive member; a tension control memberconnected to oneend of said lever and being movable between positionsfor selectively increasing and decreasing the tension in said strandmeans, and biasing means urging said tension control member to a neutralposition; brake means operable on the other end of said lever responsiveto actuation of said tram ming means; whereby, during tramming actuationof said tail section, strand tension is maintained at its value at thebeginning of such tramming actuation.

No references cited.

